update docs: a variable was renamed to keep the
C and C++ versions in sync

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>

marginlabels were improperly used instead of
subsubsections

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>

Ticket #8



Finally move the documentation to track the
RFC6330 namespace for both C and C++ APIs

fixes are related to the documentation
* decode_symbol was forgotten
* future_state uniformed between RAW and RFC
* renamed a couple of RaptorQ__v1 in RFC6330__v1

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>